Electrical remodeling of the diseased heart is characterized by profound changes in ion channel activity that contributes to contractile dysfunction and arrhythmic sudden death in heart failure patients. Our laboratory has shown that oxidative stress underlies K+ channel remodeling in the rat heart with chronic infarction through redox-mediated mechanisms. Preliminary data further suggest that these mechanisms involve thiol oxidoreductase systems whose primary biological role is to protect cellular proteins from oxidative damage. The thioredoxin system, which is composed of thioredoxin, thioredoxin reductase and NADPH, is a major oxidoreductase network affecting cardiovascular function, but its role in regulating ion channels is not known. The present project will fill this gap in knowledge by testing the central hypothesis that remodeling of K+ channels in the failing heart involves impairment of the thioredoxin system that normally functions as a repair mechanism to protect cell proteins from oxidative damage. The specific aims of the proposed studies are to: 1) define the electrophysiological function of the thioredoxin system in the ventricle, and 2) identify cellular mechanisms that regulate the thioredoxin system and determine their impact on K+ channel remodeling. Isolated ventricular myocytes from rat and mouse hearts with chronic myocardial infarction will be used as the primary experimental tool to study redox-related factors controlling pathogenic electrical remodeling. Studies will include a comparison of the impact of chronic infarction on transgenic mice with cardiac-specific depletion or over-expression of thioredoxin. The primary focus of our experiments will be on mechanisms involved in the remodeling of K+ channels underlying the transient outward current, Ito, which will be examined by the patch-clamp technique. Electrophysiological data will be correlated with molecular studies of K+ channel ?-subunit expression, as well as biochemical and molecular analyses of the activity/expression of thioredoxin and its up-stream regulator, thioredoxin reductase. This project will explore fundamental, biological processes that regulate cardiac ion channel activity and establish a basic framework for therapies aimed at preventing or reversing pathogenic electrical remodeling in the failing heart. Lay summary Experimental studies of heart failure suggest that damage to cellular proteins causes specific defects in ion channels of heart muscle cells that contribute to the progression of heart failure and lead to arrhythmias. This proposal will explore the function and regulation of an intrinsic protein repair system and determine its ability to reverse abnormal ion channel activity in the failing heart. These studies will provide new insights into the causes of the cell damage and abnormal electrical activity in heart failure, and identify therapeutic strategies to prevent or reverse cardiac dysfunction. PHS 398 (Rev. 09/04) Page 2 Principal Investigator/Program Director (Last, first, middle): Rozanski, George, J